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Fraser
2006-Dec-22, 08:46 PM
To see any distance in space, you need some kind of telescope. We've got some pretty powerful ones here on Earth, but nature has us beat with gravitational lenses. ...

Read the full blog entry (http://www.universetoday.com/2006/12/22/use-galactic-gravitational-lenses-to-really-see-the-universe/)

pantzov
2006-Dec-22, 11:21 PM
i find that whenever i look at new field views these days i am always looking for lensing. it has become such an important part of modern observation.

barsuhn
2006-Dec-25, 11:39 PM
I agree that is an important field but there iare still msiing some simple examples on how such a gravitational lens works. Most articles try to answer the question WHY it works: The reader is then lead to the field of general relativity and gets lost somewhere. That is comparable to asking a child that uses a lens to burn a hole into a sheet of paper, should at first study the theory of electromagbetoc waves. I expect that people that have understood the principles of gravitational lensing should be able to sketch some ray tracing graphics that copuld be understood without a knoeledge of general relativity.
All the best Jurgen

Gerald Lukaniuk
2006-Dec-26, 03:18 AM
How much of our view of the universe is distorted by gravitational lensing and perhaps relensing of a further distorted image? Our whole cosmology might be thrown off.

Shahbaz
2006-Dec-26, 05:46 AM
I am not very good in optics but have adequate knowledge of general relativity, as far as physics is concerned.

Now, can anyone explain me how does bending of light magnifies?

antoniseb
2006-Dec-26, 02:59 PM
can anyone explain me how does bending of light magnifies?

First, concerning barsuhn's request, there was a paper that we linked to in the astronomy section a few weeks ago about deconvolving the images of a quasar and host galaxy from the gravitational lens that it passed through. It was a fairly complex chore to accomplish, and left some ambiguities in the flattened image, but it worked, and also told quite a bit about the lensing galaxy.

Second, as to why the bending of light magnifies, this is probably better understood in the simpler case of microlensing, in which the light from learly a point source is bent by something that has a nearly spherically symmetric field around it. In this case when the source and lens line up nearly with us, we see light from the source which has bent in many different ways around the lensing object and comes to us. As the alignment gets better, we see a much brighter source. If we could see with high enough resolution we'd see the source look like an arc or a ring instead of the nearly point source that it normally looks like. So what we are seeing really, is a magnification of light-gathering power, not of image size in an easily interpreted way.

John Mendenhall
2006-Dec-26, 03:34 PM
I am not very good in optics but have adequate knowledge of general relativity, as far as physics is concerned.

Now, can anyone explain me how does bending of light magnifies?

Try here, also.

http://en.wikipedia.org/wiki/Gravitational_lensing

barsuhn
2006-Dec-30, 05:54 AM
Thank you for the link to Wikipedia, John. So far I have the impression that the comparison of a gravitational "lens" with an optical lens is misleading. If in the case of an optical lens parallel rays arrive perpendicular to the plane of the lens, they are united in the focal points. Parallel rays arriving oblique to the plane of the lens are united in a point in the focal plain thus creating a real image of infinitely distant objects in the focal plane. In the laboratory you could put a screen at the focal plane and see the real image on the screen.

As far as I understand even an ideal gravitational lens resulting from a point mass has no focal point and hence no focal plane. It does not produce a real image. On the other hand a "gravitational lens" produces effects like the Einstein ring that have no counterpart at the case of the optical lens. A "gravitational lens" is by no means a lens in the sense of a lense you use in your telescopes. The term "lens" in the field of gravitation does not help understanding this gravitational effect.

A careful explanation of a gravitational lens including ray tracing starting with simple idealised cases is still missing. I do not understand why.

All the best Jurgen

bill mendenhall
2007-Jan-03, 03:59 PM
Kubelka Munk calculations for determining the Hiding power(scattering coefficients) of Titanium dioxide particles in films can lead to coordinates in Imaginary space. Generally in programming, the data has to be adjusted and recalculations done until the light scattering numbers fall in the current Universe. Perhaps the lensing is just a glimse into an alternate Universe/imaginary space. Of course if we could move a parsec or two to the left or right we might be able to see if there really is anything behind the object that is causing the lensing.

John Mendenhall
2007-Jan-03, 04:34 PM
Kubelka Munk calculations for determining the Hiding power(scattering coefficients) of Titanium dioxide particles in films can lead to coordinates in Imaginary space. Generally in programming, the data has to be adjusted and recalculations done until the light scattering numbers fall in the current Universe. Perhaps the lensing is just a glimse into an alternate Universe/imaginary space. Of course if we could move a parsec or two to the left or right we might be able to see if there really is anything behind the object that is causing the lensing.

Cool idea. Imaginary gravity? Are gravitational waves from distant objects focused by foreground objects?

Bill ist mein Bruder, Fraser, ist nicht ein 'sock puppet'. Now you've got two of us to put up with.

Gerald Lukaniuk
2007-Jan-08, 08:51 AM
Lensing is certainly a misleading term for this relativistic effect and it would best be described as an image distortion. Like all relativistic effects, bizarre counterintuitive inferences are made about the nature of ordinary objects due to the discrepancies light emanating from those objects when they exist in another frame of reference. Light that we would expect to intercept from that object would be directed elsewhere and light we would ordinarily not expect would affect our instruments leading us to assume time and space distortions that the object would not actually be experiencing.
Redirecting of light from an object directly behind a massive object might at best mimic a donut shaped lens a select point linear to the objects, information would be contradictory. While light traveling linearly from the distant object would be stopped by the intervening object its image would be composed of light redirected by the nearer object as well as that objects own radiance. Light that ordinarily would have passed through a circular area around the observer perpendicular to the alignment of the objects would could be thought as having been focused at the observer but it would also be combined with light rays emanating from a circus of more distant objects redirected by the intervening mass.
Such an effect would never happen in an optical magnifying lens. In a basic system, an enlarged view of a select central portion of the possible field of view is produced at the expense of the total field of view by redirecting light rays from that portion that ordinarily would bypass the observer. Extraneous light from beyond the field of view does not reach the observer. The redirection of light through an optical lens has reliably been explained by the changing speed of light as it moves from substances with different optical densities or indexes of refraction, the bending necessitated by light’s reluctance to lose energy to this action. There can be a bifringement or bleeding of colours as the speeds of all wavelengths are not affected equally in some substances.
There appears to be nothing in general relativity to indicate this separation of wavelength would happen passing through a gravitational field. Nor is there an indication of a reverse effect as when light leaves the lens. In an optical lens, light rays that are emitted by an object simultaneous reach the observer through the lens simultaneous although later than to another observer equidistant but bypassing the lens. Say if the object was changing colour extremely fast these two observers would record different colours for a given point in time.
A bizarre impossible to optics effect would occur if the observer of such a super fast chameleon was of the alignment in such a way that he was observing both light directly from that object combined with light of an earlier colour redirected by a massive intervening object. He could erroneously report this object as having an impossible spectrum. Or even weirder if he could discern events time would seem scrambled on this object.

Cosmo54
2007-Aug-11, 07:20 PM
I have a question about gravitational lensing. I searched online and couldn't find anything about most favored models of lens demographically.

Are there any proposals for the lens doublet model?

Definition: Lens Doublet - A pair of optical lenses having different optical qualities, such as their shapes and refractive indices used together to minimize distortion. For example, chromatic aberration from one lens may be largely canceled by the other.

Intuitively only, this model of lensing could be favorable in galactic clusters. Ok, ok - it fits my mental image of a "ball" possibly formed amidst a galaxy cluster. It seems logical. [prepared for laughter;-)]

It is difficult to fathom round not being the preferred choice in all celestial objects, in regards to gravitational influence.

A lens doublet, hanging alone, with no significant inner gravitational entities appeals to my conservative side. I suppose it would entail the sphere as more absent its own gravitational influence, as opposed to self contained influence. (negative mirror image? dark gravity?)

Note: The definition above includes differing shapes, but does exclude symmetry.

Amber Robot
2007-Aug-13, 02:40 PM
I am familiar with lens doublets, having used them in spectrographs I've worked with. (We've even used triplets and quadruplets!)

But I'm really not sure what you're asking here. In the gravitational lens model, an object, like a galaxy, or a group of objects, like a cluster of galaxies, is the lens. The gravity of the object(s) distorts the space-time around it so that light is effectively curved in its path. The curving isn't like a normal lens though, in that for a normal lens, the greatest deviation of the light is at the edges of the lens and there is zero deviation for light going through the center. A gravitational lens has the exact opposite effect.

Depending on the geometric orientation and distances between the observer, the lens, and the source, one may see multiple images of the source and/or arcs (or even complete circles when the alignment is near perfect).